The purpose of these studies is to develop a more complete understanding of the cellular and molecular lesions that result in immunodeficiency diseases. There are four main foci of research: 1) Identifying stages of developmental arrest in T lymphocytes from patients with immunodeficiencies; 2) Evaluation of cytokine and T-cell antigen receptor repertoire patterns in immunodeficiencies; 3) Examination of the maturation arrest in B lymphocytes in patients with severe combined immunodeficiency (SCID); and 4) Identifying mutations in the recombinase activating genes as the molecular pathogenesis of SCID. During the past year, we have demonstrated that neutropenia in a form of combined immunodeficiency results from excessive production of TNF-A from aberrantly-active histiocytes. We have demonstrated that the proposed TH2 T lymphocyte predominance in Omenn Syndrome is incorrect and that inflammatory TH1-type cytokines, IL-2 and INF-, are overproduced in relation to the TH2-type, anti-inflammatory cytokines, IL-4 and IL-5. Additionally, T lymphocytes present in Omenn Syndrome are oligoclonally expanded, possibly as a result of impaired apoptosis, and result in some of the pathologic features of this disorder. We have found that B lymphocytes in X-linked SCID appear to have a maturation arrest at a fetal repertoire developmental stage. This finding could explain why there is poor B lymphocyte function in X-linked SCID despite successful T lymphocyte engraftment with bone marrow transplantation. We have identified 8 patients with SCID in whom the recombinase activating gene-1 (RAG-1) could be malfunctioning. Using PCR analysis, four of the suspected patients have an abnormal amplification product at about one third the way into the gene. The entire 3 Kb gene is being sequenced from each patient, for verification of mutations. Future goals are: 1) fully explore the role of RAG-1 mutations in immunodeficiencies; 2) further explore the role of abnormal cytokine expression in causing cytopenias and immunodeficiencies; 3) examine for defects in apoptosis in Omenn Syndrome; and 4) examine for the maturation defect in X-linked SCID B lymphocytes can be overcome with cytokine co-stimulation. The results are anticipated to eventually allow better treatment of patients with immunodeficiencies.